Microscope objective

ABSTRACT

A microscope objective comprising a first lens component arranged as a positive meniscus lens, a second lens component arranged as a positive lens, a third lens component having positive refractive power, a fourth lens component having positive refractive power, a fifth lens component having negative refractive power, and a sixth lens component arranged as a cemented positive meniscus lens, the microscope objective being arranged that the working distance is extremely long, aberrations are corrected extremely favorably up to the marginal portion of field, and magnification is 40×.

BACKGROUND OF THE INVENTION

(a) Field of the Invention

The present invention relates to a microscope objective and, moreparticularly, to a microscope objective with a magnification about 40×of which the working distance is long and aberrations are favourablycorrected up to the marginal portion of field.

(b) Description of the Prior Art

Known microscope objectives with a magnification about 40×, long workingdistance and aberrations favourably corrected up to the marginal portionof the field are disclosed, for example, in Japanese publishedunexamined patent application No. 33646/72 etc. However, the workingdistance of those known microscope objectives is about 70% of the focallength, and this is insufficient when using the microscope objectives insuch manner as to give some operation to the specimen by observing itthrough a microscope. Besides, even when using the microscope objectivesin other manners, a working distance longer than the above is morepreferable because it is then convenient for use.

On the other hand, microscope objectives have such tendency thataberrations abruptly become unfavourable when it is attempted to makethe working distance long by keeping the same degree of NA and,consequently, it becomes difficult to obtain a favourable quality ofimage. Therefore, in known microscope objectives, a meniscus lens havinga concave surface with strong curvature on the image side is arranged inthe rear lens group in order to make the working distance long. However,even when the above-mentioned arrangement is made, aberrations abruptlybecome unfavourable when the working distance is made longer than acertain degree, and it becomes difficult to correct them.

Due to the above-mentioned reason, there is no known microscopeobjective of which the working distance is very long and, at the sametime, aberrations are favourably corrected up to the marginal portion offield.

SUMMARY OF THE INVENTION

It is, therefore, a primary object of the present invention to provide amicroscope objective with a magnification about 40× of which the workingdistance is extremely long, image surface is flat and aberrations arefavourably corrected up to the marginal portion of field.

The microscope objective according to the present invention comprises afirst lens component arranged as a positive meniscus lens having aconcave surface on the object side, a second lens component arranged asa positive lens, a third lens component comprising a positive lenselement and having positive refractive power as a whole, a fourth lenscomponent comprising a positive lens element and having positiverefractive power as a whole, a fifth lens component comprising anegative lens element and having negative refractive power as a whole,and a sixth lens component arranged as a cemented positive meniscuslens, the microscope objective according to the present inventionfulfilling the conditions (1) through (4) shown below:

    1.8f<|f.sub.VVI |<2.6f, f.sub.VVI <0     (1)

    1.2<r.sub.1 /r.sub.2 <1.8                                  (2)

    2<|r.sub.3 /r.sub.4 |<3.7, r.sub.3 /r.sub.4 <0 (3)

    ν.sub.IIp, ν.sub.IIIp-1 >65                          (4)

where, reference symbol f represents the focal length of the lens systemas a whole, reference symbol f_(VVI) represents the total focal lengthof the fifth and sixth lens components, reference symbols r₁ and r₂respectively represent radii of curvature of the surface on the objectside and surface on the image side of the first lens component,reference symbols r₃ and r₄ respectively represent radii of curvature ofthe surface on the object side and surface on the image side of thesecond lens component, reference symbol ν_(IIp) represents Abbe's numberof the positive lens constituting the second lens component, andreference symbol ν_(IIIp-1) represents Abbe's number of the firstpositive lens element counted from the object side in the third lenscomponent.

By adopting the above-mentioned lens configuration and arranging tofulfill the respective conditions shown in the above, the presentinvention enables to obtain a microscope objective with an extremelylong working distance and aberrations corrected favourably up to themarginal portion of field which is the primary object of the presentinvention.

The condition (1) is established in order to materialize a microscopeobjective having an extremely long working distance which is an objectof the present invention. That is, by selecting the total focal lengthf_(VVI) of the fifth and sixth lens components constituting the rearlens group as a negative value within a certain range as shown by thecondition (1), it is arranged to obtain a microscope objective with anextremely long working distance which is an object of the presentinvention.

If |f_(VVI) | becomes larger than the upper limit of the condition (1),the negative refractive power of the fifth and sixth lens components asa whole becomes weak, and it is impossible to ensure a satisfactorilylong working distance. If |f_(VVI) | becomes smaller than the lowerlimit of the condition (1), the negative refractive power of the fifthand sixth lens components as a whole becomes too strong. As a result,Petzval's sum and spherical aberrations are overcorrected and, when itis attempted to correct them by other lens components, it becomesdifficult to correct offaxial aberrations such as coma etc.

The conditions (2) and (3) are established in order to minimizespherical aberration to be caused by the front lens group comprising thefirst, second, third and fourth lens components. If the condition (2)and/or (3) are not fulfilled, the correction coefficients of surfacesr₁, r₂, r₃ and r₄ for spherical aberration do not become uniform, andthe correction coefficient of some of said surfaces becomes large. As aresult, spherical aberration caused by the surface becomes remarkablylarge, and it becomes impossible to correct spherical aberration by therear lens group.

The condition (4) is established in order to make longitudinal chromaticaberration small and, especially, to make the secondary spectrum small.If the condition (4) is not fulfilled, the secondary spectrum becomeslarge.

Besides the conditions described so far, it is preferable to arrangethat the microscope objective according to the present invention furtherfulfills the conditions (5) and (6) shown below: ##EQU1## where,reference symbol r₁₂ represents the radius of curvature of the surfaceon the object side of the fifth lens component, reference symbol r₁₇represents the radius of curvature of the surface on the image side ofthe sixth lens component, reference symbol n_(V-1) represents therefractive index of the first negative lens element counted from theobject side in the fifth lens component, and reference symbol n_(VI-2)represents the refractive index of the second negative lens elementcounted from the object side in the sixth lens component.

The conditions (5) and (6) are established in order to make sphericalaberration, which is minimized by fulfilling the conditions (2) and (3)still smaller, and to correct offaxial aberrations at the same time.

The condition (5) is established in order to chiefly correct sphericalaberration and relates to the surface r₁₂. If the value defined by thecondition (5) becomes larger than the upper limit thereof, sphericalaberration will be undercorrected. If it is attempted to correct saidspherical aberration by means of other lens surfaces, offaxialaberrations become unfavourable and it is difficult to correct them. Ifthe value defined by the condition (5) becomes smaller than the lowerlimit thereof, Petzval's sum becomes a negative value with a largeabsolute value, and curvature of field will be overcorrected.

The condition (6) is established in order to chiefly correct offaxialaberrations and, especially, to correct coma. If the value defined bythe condition (6) becomes larger than the upper limit thereof or smallerthan the lower limit thereof, it becomes difficult to favourably correctcoma, which is caused by the first through the fourth lens components,without disturbing the symmetry of coma and, at the same time, bykeeping favourable balance with spherical aberration.

When paraxial aberrations and offaxial aberrations are corrected byfulfilling the conditions (5) and (6) shown in the above, sphericalaberration of the secondary spectrum will be largely overcorrected. Tocorrect said spherical aberration of the secondary spectrum, it ispreferable to arrange that the microscope objective according to thepresent invention further fulfills the conditions (7) through (10) shownbelow:

    f<r.sub.13 <2f                                             (7)

    ν.sub.Vp -ν.sub.Vn >40                               (8)

    f<|r.sub.16 |<2f, r.sub.16 <0            (9)

    ν.sub.VIn -ν.sub.VIp >20                             (10)

where, reference symbol r₁₃ represents the radius of curvature of thecemented surface of the fifth lens component, reference symbol r₁₆represents the radius of curvature of the cemented surface of the sixthlens component, reference symbols ν_(Vp) and ν_(Vn) respectivelyrepresent Abbe's numbers of the positive and negative lens elementsconstituting the fifth lens component, and reference symbols ν_(VIp) andν_(VIn) respectively represent Abbe's numbers of the positive andnegative lens elements constituting the sixth lens component.

If any of the above-mentioned conditions is not fulfilled, it isdifficult to correct spherical aberration of the secondary spectrum,longitudinal chromatic aberration and lateral chromatic aberration inwell balanced state.

If r₁₃ becomes larger than the upper limit of the condition (7) and/or|r₁₆ | becomes smaller than the lower limit of the condition (9),spherical aberration of the secondary spectrum will be overcorrected andlongitudinal chromatic aberration will be undercorrected. On thecontrary, if r₁₃ becomes smaller than the lower limit of the condition(7) and/or |r₁₆ | becomes larger than the upper limit of the condition(9), spherical aberration of the secondary spectrum will beundercorrected and longitudinal chromatic aberration will beovercorrected. Consequently, balance of said aberrations becomesunsatisfactory.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a sectional view of Embodiments 1 through 4 of themicroscope objective according to the present invention;

FIG. 2 shows a sectional view of Embodiment 5 of the microscopeobjective according to the present invention;

FIGS. 3 through 7 respectively show graphs illustrating aberrationcurves of Embodiments 1 through 5 of the present invention; and

FIGS. 8 and 9 respectively show graphs illustrating aberration curves ofEmbodiment 1 when different thicknesses of cover glasses are used.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, preferred embodiments of the microscope objective according to thepresent invention are shown below.

    ______________________________________                                        Embodiment 1                                                                  f = 1,  NA = 0.5,  β = -40X,  WD = 2.206                                 ______________________________________                                        r.sub.1 = -3.4982                                                             d.sub.1 = 0.662                                                                              n.sub.1 = 1.7725                                                                           ν.sub.1 = 49.66                                r.sub.2 = -2.2539                                                             d.sub.2 = 0.052                                                               r.sub.3 = 10.9273                                                             d.sub.3 = 0.706                                                                              n.sub.2 = 1.497                                                                            ν.sub.2 = 81.61                                r.sub.4 = -3.8062                                                             d.sub.4 = 0.392                                                               r.sub.5 = 7.4367                                                              d.sub.5 = 1.396                                                                              n.sub.3 = 1.43389                                                                          ν.sub.3 = 95.15                                r.sub.6 = -2.7803                                                             d.sub.6 = 0.429                                                                              n.sub.4 = 1.6445                                                                           ν.sub.4 = 40.8                                 r.sub.7 = 2.41                                                                d.sub.7 = 1.02 n.sub.5 = 1.6779                                                                           ν.sub.5 = 55.33                                r.sub.8 = -6.1119                                                             d.sub.8 = 0.392                                                               r.sub.9 = 3.4966                                                              d.sub.9 = 1.203                                                                              n.sub.6 = 1.497                                                                            ν.sub.6 = 81.61                                r.sub.10 = -4.13                                                              d.sub.10 = 0.492                                                                             n.sub.7 = 1.74                                                                             ν.sub.7 = 31.7                                 r.sub.11 = 9.1009                                                             d.sub.11 = 1.151                                                              r.sub.12 = -3.4885                                                            d.sub.12 = 0.183                                                                             n.sub.8 = 1.71736                                                                          ν.sub.8 = 29.51                                r.sub.13 = 1.6744                                                             d.sub.13 = 0.34                                                                              n.sub.9 = 1.497                                                                            ν.sub.9 = 81.61                                r.sub.14 = 32.062                                                             d.sub.14 = 0.026                                                              r.sub.15 = 1.8617                                                             d.sub.15 = 0.745                                                                             n.sub.10 = 1.78472                                                                         ν.sub.10 = 25.68                               r.sub.16 = -1.6982                                                            d.sub.16 = 0.719                                                                             n.sub.11 = 1.726                                                                           ν.sub.11 = 53.56                               r.sub.17 = 1.216                                                              |f.sub.VVI | = 2.22, r.sub.1 /r.sub.2 = 1.55,               |r.sub. 3 /r.sub.4 | = 2.87                                 |r.sub.12 /(n.sub.V-1 - 1)| = 4.86, |r.sub.17      /(1 - n.sub.VI-2)| = 1.68                                            ______________________________________                                         thickness of cover glass = 0.262                                         

    ______________________________________                                        Embodiment 2                                                                  f = 1,  NA = 0.5,  β = -40X,  WD = 2.236                                 ______________________________________                                        r.sub.1 = -3.1627                                                             d.sub.1 = 0.663                                                                              n.sub.1 = 1.7725                                                                           ν.sub.1 = 49.66                                r.sub.2 = -2.244                                                              d.sub.2 = 0.05                                                                r.sub.3 = 10.4467                                                             d.sub.3 = 0.728                                                                              n.sub.2 = 1.497                                                                            ν.sub.2 = 81.61                                r.sub.4 = -4.3406                                                             d.sub.4 = 0.197                                                               r.sub.5 = 6.4547                                                              d.sub.5 = 1.424                                                                              n.sub.3 = 1.43389                                                                          ν.sub.3 = 95.15                                r.sub.6 = -3.0048                                                             d.sub.6 = 0.454                                                                              n.sub.4 = 1.6445                                                                           ν.sub.4 = 40.8                                 r.sub.7 = 2.7084                                                              d.sub.7 = 1.023                                                                              n.sub.5 = 1.6779                                                                           ν.sub.5 = 55.33                                r.sub.8 = -5.5653                                                             d.sub.8 = 0.34                                                                r.sub.9 = 3.6181                                                              d.sub.9 = 1.247                                                                              n.sub.6 = 1.497                                                                            ν.sub.6 = 81.61                                r.sub.10 = -4.89                                                              d.sub.10 = 0.519                                                                             n.sub.7 = 1.74                                                                             ν.sub.7 = 31.7                                 r.sub.11 = 9.1935                                                             d.sub.11 = 1.19                                                               r.sub.12 = -2.7454                                                            d.sub.12 = 0.21                                                                              n.sub.8 = 1.71736                                                                          ν.sub.8 = 29.51                                r.sub.13 = 1.286                                                              d.sub.13 = 0.277                                                                             n.sub.9 = 1.497                                                                            ν.sub.9 = 81.61                                r.sub.14 = -168.3923                                                          d.sub.14 = 0.026                                                              r.sub.15 = 1.7001                                                             d.sub.15 = 0.775                                                                             n.sub.10 = 1.78472                                                                         ν.sub.10 = 25.71                               r.sub.16 = -1.5008                                                            d.sub.16 = 0.776                                                                             n.sub.11 = 1.726                                                                           ν.sub.11 = 53.56                               r.sub.17 = 1.2095                                                             |f.sub.VVI | = 2.03, r.sub.1 /r.sub.2 = 1.42,               | r.sub.3 /r.sub.4 | = 2.41                                 |r.sub.12 /(n.sub.V-1 -1)| = 3.83, |r.sub.17       /(1 -n.sub.VI-2)| = 1.67                                             ______________________________________                                         thickness of cover glass = 0.262                                         

    ______________________________________                                        Embodiment 3                                                                  f = 1,  NA = 0.5,  β = -40X,  WD = 2.232                                 ______________________________________                                        r.sub.1 = -3.4901                                                             d.sub.1 = 0.662                                                                              n.sub.1 = 1.7725                                                                           ν.sub.1 = 49.66                                r.sub.2 = -2.2332                                                             d.sub.2 = 0.05                                                                r.sub.3 = 8.8889                                                              d.sub.3 = 0.727                                                                              n.sub.2 = 1.497                                                                            ν.sub.2 = 81.61                                r.sub.4 = -4.0044                                                             d.sub.4 = 0.197                                                               r.sub.5 = 7.9819                                                              d.sub.5 = 1.422                                                                              n.sub.3 = 1.43389                                                                          ν.sub.3 = 95.15                                r.sub.6 = -2.824                                                              d.sub.6 = 0.453                                                                              n.sub.4 = 1.6445                                                                           ν.sub.4 = 40.8                                 r.sub.7 = 2.3314                                                              d.sub.7 = 1.022                                                                              n.sub.5 = 1.6779                                                                           ν.sub.5 = 55.33                                r.sub.8 = -6.9004                                                             d.sub.8 = 0.339                                                               r.sub.9 = 3.6048                                                              d.sub.9 = 1.246                                                                              n.sub.6 = 1.497                                                                            ν.sub.6 = 81.61                                r.sub.10 = -4.2614                                                            d.sub.10 = 0.518                                                                             n.sub.7 = 1.74                                                                             ν.sub.7 = 31.7                                 r.sub.11 = 9.972                                                              d.sub.11 = 1.189                                                              r.sub.12 = -3.3423                                                            d.sub.12 = 0.209                                                                             n.sub.8 = 1.71736                                                                          ν.sub.8 = 29.51                                r.sub.13 = 1.5201                                                             d.sub.13 = 0.276                                                                             n.sub.9 = 1.497                                                                            ν.sub.9 = 81.61                                r.sub.14 = -222.3991                                                          d.sub.14 = 0.026                                                              r.sub.15 = 1.8581                                                             d.sub.15 = 0.774                                                                             n.sub.10 = 1.78472                                                                         ν.sub.10 = 25.68                               r.sub.16 = -1.6017                                                            d.sub.16 = 0.774                                                                             n.sub.11 = 1.726                                                                           ν.sub.11 = 53.56                               r.sub.17 = 1.2426                                                             |f.sub.VVI | = 2.29, r.sub.1 /r.sub.2 = 1.56,               | r.sub.3 /r.sub.4 | = 2.22                                 |r.sub.12 /(n.sub.V-1 - 1)| = 4.66, |r.sub.17      /(1 - n.sub.VI-2)| = 1.71                                            ______________________________________                                         thickness of cover glass = 0.261                                         

    ______________________________________                                        Embodiment 4                                                                  f = 1,  NA = 0.5,  β = -40X,  WD = 2.186                                 ______________________________________                                        r.sub.1 = -3.5714                                                             d.sub.1 = 0.663                                                                              n.sub.1 = 1.7725                                                                           ν.sub.1 = 49.66                                r.sub.2 = -2.2337                                                             d.sub.2 = 0.327                                                               r.sub.3 = 13.0111                                                             d.sub.3 = 0.678                                                                              n.sub.2 = 1.497                                                                            ν.sub.2 = 81.61                                r.sub.4 = -3.8674                                                             d.sub.4 = 0.342                                                               r.sub.5 = 7.47                                                                d.sub.5 = 1.374                                                                              n.sub.3 = 1.43389                                                                          ν.sub.3 = 95.15                                r.sub.6 = -2.8644                                                             d.sub.6 = 0.404                                                                              n.sub.4 = 1.6445                                                                           ν.sub.4 = 40.8                                 r.sub.7 = 2.4542                                                              d.sub.7 = 1    n.sub.5 = 1.6779                                                                           ν.sub.5 = 55.33                                r.sub.8 = -6.105                                                              d.sub.8 = 0.393                                                               r.sub.9 = 3.3165                                                              d.sub.9 = 1.198                                                                              n.sub.6 = 1.497                                                                            ν.sub.6 = 81.61                                r.sub.10 = -4.4735                                                            d.sub.10 = 0.469                                                                             n.sub.7 = 1.74                                                                             ν.sub.7 = 31.7                                 r.sub.11 = 7.302                                                              d.sub.11 = 1.13                                                               r.sub.12 = -3.4543                                                            d.sub.12 = 0.183                                                                             n.sub.8 = 1.71636                                                                          ν.sub.8 = 29.51                                r.sub.13 = 1.891                                                              d.sub.13 = 0.341                                                                             n.sub.9 = 1.497                                                                            ν.sub.9 = 81.61                                r.sub.14 = 18.8426                                                            d.sub.14 = 0.026                                                              r.sub.15 = 1.8343                                                             d.sub.15 = 0.725                                                                             n.sub.10 = 1.78472                                                                         ν.sub.10 = 25.68                               r.sub.16 = -1.8322                                                            d.sub.16 = 0.699                                                                             n.sub.11 = 1.726                                                                           ν.sub.11 = 53.56                               r.sub.17 = 1.1646                                                             |f.sub.VVI | = 2.13, r.sub.1 /r.sub.2 = 1.6, |     r.sub.3 /r.sub.4 | = 3.36                                            |r.sub.12 /(n.sub.V-1 - 1)| = 4.82, |r.sub.17      /(1 - n.sub.VI-2)| = 1.6                                             ______________________________________                                         thickness of cover glass = 0.262                                         

    ______________________________________                                        Embodiment 5                                                                  f = 1,  NA = 0.5,  β = -40X,  WD = 2.208                                 ______________________________________                                        r.sub.1 = -3.4749                                                             d.sub.1 = 0.662                                                                              n.sub.1 = 1.76647                                                                          ν.sub.1 = 37.03                                r.sub.2 = -2.2884                                                             d.sub.2 = 0.05                                                                r.sub.3 = 9.7628                                                              d.sub.3 = 0.702                                                                              n.sub.2 = 1.497                                                                            ν.sub.2 = 81.61                                r.sub.4 = -3.6774                                                             d.sub.4 = 0.392                                                               r.sub.5 = 7.5333                                                              d.sub.5 = 1.397                                                                              n.sub.3 = 1.43389                                                                          ν.sub.3 = 95.15                                r.sub.6 = -2.6362                                                             d.sub.6 = 0.428                                                                              n.sub.4 = 1.63599                                                                          ν.sub.4 = 36.59                                r.sub.7 = 2.444                                                               d.sub.7 = 0.997                                                                              n.sub.5 = 1.68188                                                                          ν.sub.5 = 48.89                                r.sub.8 = -6.0685                                                             d.sub.8 = 0.392                                                               r.sub.9 = 3.618                                                               d.sub.9 = 0.471                                                                              n.sub.6 = 1.49791                                                                          ν.sub.6 = 55.84                                r.sub.9 ' = 2.5286                                                            d.sub.9 ' = 0.968                                                                            n.sub.6 '= 1.497                                                                           ν.sub.6 ' = 81.61                              r.sub.10 = -2.9389                                                            d.sub.10 = 0.493                                                                             n.sub.7 = 1.75001                                                                          ν.sub.7 = 28.27                                r.sub.11 = 9.0927                                                             d.sub.11 = 0.936                                                              r.sub.12 = -3.4568                                                            d.sub.12 = 0.183                                                                             n.sub.8 = 1.70991                                                                          ν.sub.8 = 30.86                                r.sub.13 = 1.7111                                                             d.sub.13 = 0.34                                                                              n.sub.9 = 1.497                                                                            ν.sub.9 = 81.61                                r.sub.14 = 37.4012                                                            d.sub.14 = 0.026                                                              r.sub.15 = 1.8973                                                             d.sub.15 = 0.749                                                                             n.sub.10 = 1.80265                                                                         ν.sub.10 = 25.11                               r.sub.16 = -1.6842                                                            d.sub.16 = 0.724                                                                             n.sub.11 = 1.71559                                                                         ν.sub.11  = 55.05                              r.sub.17 = 1.1841                                                             |f.sub.VVI | = 2.39, r.sub.1 /r.sub.2 = 1.52,               |r.sub.3 /r.sub.4 | = 2.65                                  |r.sub.12 /(n.sub.V-1 - 1)| = 4.87, |r.sub.17      /(1 - n.sub.VI-2)| =1.65                                             ______________________________________                                         thickness of cover glass = 0.262                                         

In embodiments shown in the above, reference symbols r₁ through r₁₇respectively represent radii of curvature of respective lens surfaces,reference symbols d₁ through d₁₆ respectively represent thicknesses ofrespective lenses and airspaces between respective lenses, referencesymbols n₁ though n₁₁ respectively represent refractive indices ofrespective lenses, and reference symbols ν₁ through ν₁₁ respectivelyrepresent Abbe's numbers of respective lenses.

Out of respective embodiments shown in the above, Embodiment 1 has thelens configuration as shown in FIG. 1 and its aberration curves are asshown in FIG. 3.

The microscope objective according to Embodiment 1 is arranged that itis possible to correct aggravation of aberrations, which occurs whendifferent thicknesses of cover glasses are used, by adjusting theairspace d₈ between the third and fourth lens components.

For example, by adjusting said airspace as d₈ =0.157 when the thicknessof cover glass is 0 mm (when a cover glass is not used) and as d₈ =0.664when the thickness of cover glass is 2 mm, it is possible to maintainthe favourable states of aberrations as shown in FIGS. 8 and 9respectively.

The lens systems according to Embodiments 2, 3 and 4 also have the lensconfiguration as shown in FIG. 1. Out of them, Embodiments 2 and 3 arearranged that it is possible to correct aggravation of aberrations,which occurs due to variation in the thickness of cover glass, byadjusting the airspace between the third and fourth lens components.Embodiment 4 is arranged that it is possible to correct aggravation ofaberrations, which occurs due to variation in the thickness of coverglass, by adjusting the airspace d₂ between the first and second lenscomponents and the airspace d₈ between the third and fourth lenscomponents or by adjusting only the airspace d₈ between the third andfourth lens components.

The lens system according to Embodiment 5 has the lens configuration asshown in FIG. 2. That is, the fourth lens component is arranged as acemented lens component formed by cementing three lens elementstogether. The lens system according to Embodiment 5 is also arrangedthat it is possible to correct aggravation of aberrations, which occursdue to variation in the thickness of cover glass, by adjusting theairspace d₈ between the third and fourth lens components.

Aberrations curves of said Embodiments 2 through 5 are as shown in FIGS.4 through 7 respectively.

As described so far and as it will be evident from respectiveembodiments, the microscope objective according to the present inventionis arranged that the working distance is extremely long, aberrations arefavourably corrected up to the marginal portion of field, and quality ofimage is excellent. The working distances WD of respective embodimentsare WD=2.206 for Embodiment 1, WD=2.236 for Embodiment 2, WD=2.232 forEmbodiment 3, WD=2.186 for Embodiment 4, and WD=2.208 for Embodiment 5and are remarkably longer than those of known microscope objectives withmagnifications about 40× which are considered to have long workingdistances. For example, the microscope objective disclosed in Japanesepublished unexamined patent application No. 33646/72 has the workingdistance about 0.71. Compared with said known microscope objective, theworking distance of the microscope objective according to the presentinvention is extremely long. Besides, aberrations of the microscopeobjective according to the present inveniton are corrected extremelyfavourably as it will be evident from FIGS. 3 through 7.

I claim:
 1. A microscope objective comprising a first lens componentarranged as a positive meniscus lens having a concave surface on theobject side, a second lens component arranged as a positive lens, athird lens component comprising a positive lens element and havingpositive refractive power as a whole, a fourth lens component comprisinga positive lens element and having positive refractive power as a whole,a fifth lens component comprising a negative lens element and havingnegative refractive power as a whole, and a sixth lens componentarranged as a cemented positive meniscus lens, said microscope objectivebeing arranged to fulfill the conditions (1) through (6) shown below:##EQU2## where, reference symbol f represents the focal length of thelens system as a whole, reference symbol f_(VVI) represents the totalfocal length of the fifth and sixth lens components, reference symbolsr₁ and r₂ respectively represent radii of curvature of the surface onthe object side and surface on the image side of the first lenscomponent, reference symbols r₃ and r₄ respectively represent radii ofcurvature of the surface on the object side and surface on the imageside of the second lens component, reference symbol ν_(IIp) representsAbbe's number of the positive lens constituting the second lenscomponent, and reference symbol ν_(IIIp-1) represents Abbe's number ofthe first positive lens element counted from the object side in thethird lens component, reference symbol r₁₂ represents the radius ofcurvature of the surface on the object side of the fifth lens component,reference symbol n_(V-1) represents the refractive index of the firstnegative lens element counted from the object side in the fifth lenscomponent, reference symbol r₁₇ represents the side of the sixth lenscomponent, and reference symbol n_(VI-2) represents the refractive indexof the second negative lens element counted from the object side in thesixth lens component.
 2. A microscope objective according to claim 1further fulfilling the conditions (7) through (10) shown below:

    f<r.sub.13 <2f                                             (7)

    ν.sub.Vp -ν.sub.Vn >40                               (8)

    f<|r.sub.16 |<2f, r.sub.16 <0            (9)

    ν.sub.VIn -ν.sub.VIp >20                             (10)

where, reference symbol r₁₃ represents the radius of curvature of thecemented surface on the fifth lens component, reference symbol r₁₆represents the radius of curvature of the cemented surrace of the sixthlens component, reference symbols ν_(Vp) and ν_(Vn) respectivelyrepresent Abbe's numbers of the positive and negative lens elementsconstituting the fifth lens component, and reference symbols ν_(VIp) andν_(VIn) respectively represents Abbe's numbers of the positive andnegative lens elements constituting the sixth lens component.
 3. Amicroscope objective according to claim 2 wherein said third lenscomponent is arranged as a cemented lens component consisting of threelens elements which are a positive, negative and positive lens elementscemented together, said fourth lens component is arranged as a positivecemented doublet consisting of a positive and negative lens elements,and said fifth lens component is arranged as a negative cemented doubletconsisting of a negative and positive lens elements, and wherein saidmicroscope objective has the following numerical data:

    ______________________________________                                        f = 1,  NA = 0.5,  β = -40X,  WD = 2.206                                 ______________________________________                                        r.sub.1 = -3.4982                                                             d.sub.1 = 0.662                                                                              n.sub.1 = 1.7725                                                                           ν.sub.1 = 49.66                                r.sub.2 = -2.2539                                                             d.sub.2 = 0.052                                                               r.sub.3 = 10.9273                                                             d.sub.3 = 0.706                                                                              n.sub.2 = 1.497                                                                            ν.sub.2 = 81.61                                r.sub.4 = -3.8062                                                             d.sub.4 = 0.392                                                               r.sub.5 = 7.4367                                                              d.sub.5 = 1.396                                                                              n.sub.3 = 1.43389                                                                          ν.sub.3 = 95.15                                r.sub.6 = -2.7803                                                             d.sub.6 = 0.429                                                                              n.sub.4 = 1.6445                                                                           ν.sub.4 = 40.8                                 r.sub.7 = 2.41                                                                d.sub.7 = 1.02 n.sub.5 = 1.6779                                                                           ν.sub.5 = 55.53                                r.sub.8 = -6.1119                                                             d.sub.8 = 0.392                                                               r.sub.9  = 3.4966                                                             d.sub.9 = 1.203                                                                              n.sub.6 = 1.497                                                                            ν.sub.6 = 81.61                                r.sub.10 = -4.13                                                              d.sub.10 = 0.492                                                                             n.sub.7 = 1.74                                                                             ν.sub.7 = 31.7                                 r.sub.11 = 9.1009                                                             d.sub.11 = 1.151                                                              r.sub.12 = -3.4885                                                            d.sub.12 = 0.183                                                                             n.sub.8 = 1.71736                                                                          ν.sub.8 = 29.51                                r.sub.13 = 1.6744                                                             d.sub.13 = 0.34                                                                              n.sub.9 = 1.497                                                                            ν.sub.9 = 81.61                                r.sub.14 = 32.062                                                             d.sub.14 = 0.026                                                              r.sub.15 = 1.8617                                                             d.sub.15 = 0.475                                                                             n.sub.10 = 1.78472                                                                         ν.sub.10 = 25.68                               r.sub.16 = -1.6982                                                            d.sub.16 = 0.719                                                                             n.sub.11 = 1.726                                                                           ν.sub.11 = 53.56                               r.sub.17 = 1.216                                                              |f.sub.VVI | = 2.22, r.sub.1 /r.sub.2 = 1.55,               |r.sub.3 /r.sub.4 | = 2.87                                  |r.sub.12 /(n.sub.V-1 - 1)| = 4.86, |r.sub.17      /(1 - n.sub.VI-2)| = 1.68                                            ______________________________________                                    

where, reference symbols r₁ through r₁₇ respectively represent radii ofcurvature of respective lens surfaces, reference symbols d₁ through d₁₆respectively represent thicknesses of respective lenses and airspacesbetween respective lenses, reference symbols n₁ through n₁₁ respectivelyrepresent refractive indices of respective lenses, and reference symbolsν₁ through ν₁₁ respectively represent Abbe's numbers of respectivelenses.
 4. A microscope objective according to claim 2 wherein saidthird lens component is arranged as a cemented lens component consistingof three lens elements which are a positive, negative and positive lenselements cemented together, said fourth lens component is arranged as apositive cemented doublet consisting of a positive and negative lenselements, and said fifth lens component is arranged as a negativecemented doublet consisting of a negative and positive lens elements,and wherein said microscope objective has the following numerical data:

    ______________________________________                                        f = 1,  NA = 0.5,  β = -40X,  WD = 2.236                                 ______________________________________                                        r.sub.1 = -3.1627                                                             d.sub.1 = 0.663                                                                              n.sub.1 = 1.7725                                                                           ν.sub.1 = 49.66                                r.sub.2 = -2.244                                                              d.sub.2 = 0.05                                                                r.sub.3 = 10.4467                                                             d.sub.3 = 0.728                                                                              n.sub.2 = 1.497                                                                            ν.sub.2 = 81.61                                r.sub.4 = -4.3406                                                             d.sub.4 = 0.197                                                               r.sub.5 = 6.4547                                                              d.sub.5 = 1.424                                                                              n.sub.3 = 1.43389                                                                          ν.sub.3 = 95.15                                r.sub.6 = -3.0048                                                             d.sub.6 = 0.454                                                                              n.sub.4 = 1.6445                                                                           ν.sub.4 = 40.8                                 r.sub.7 = 2.7084                                                              d.sub.7 = 1.023                                                                              n.sub.5 = 1.6779                                                                           ν.sub.5 = 55.33                                r.sub.8 = -5.5653                                                             d.sub.8 = 0.34                                                                r.sub.9 =  3.6181                                                             d.sub.9 = 1.247                                                                              n.sub.6 = 1.497                                                                            ν.sub.6 = 81.61                                r.sub.10 = -4.89                                                              d.sub.10 = 0.519                                                                             n.sub.7 = 1.74                                                                             ν.sub.7 = 31.7                                 r.sub.11 = 9.1935                                                             d.sub.11 = 1.19                                                               r.sub.12 = -2.7454                                                            d.sub.12 = 0.21                                                                              n.sub.8 = 1.71736                                                                          ν.sub.8 = 29.51                                r.sub.13 = 1.286                                                              d.sub.13 = 0.277                                                                             n.sub.9 = 1.497                                                                            ν.sub.9 = 81.61                                r.sub.14 = -168.3923                                                          d.sub.14 = 0.026                                                              r.sub.15 = 1.7001                                                             d.sub.15 = 0.775                                                                             n.sub.10 = 1.78472                                                                         ν.sub.10 = 25.71                               r.sub.16 = -1.5008                                                            d.sub.16 = 0.776                                                                             n.sub.11 = 1.726                                                                           ν.sub.11 = 53.56                               r.sub.17 = 1.2095                                                             |f.sub.VVI | = 2.03, r.sub.1 /r.sub.2 = 1.42,               |r.sub.3 /r.sub.4 | = 2.41                                  |r.sub.12 /(n.sub.V-1 - 1)| = 3.83, |r.sub.17      /(1 - n.sub.VI-2)| = 1.67                                            ______________________________________                                    

where, reference symbols r₁ through r₁₇ respectively represent radii ofcurvature of respective lens surfaces, reference symbols d₁ through d₁₆respectively represent thicknesses of respective lenses and airspacesbetween respective lesnes, reference symbols n₁ through n₁₁ respectivelyrepresent refractive indices of respective lenses, and reference symbolsν₁ through ν₁₁ respectively represent Abbe's numbers of respectivelenses.
 5. A microscope objective according to claim 2 wherein saidthird lens component is arranged as a cemented lens component consistingof three lens elements which are a positive, negative and positive lenselements cemented together, said fourth lens component is arranged as apositive cemented doublet consisting of a positive and negative lenselements, and said fifth lens component is arranged as a negativecemented doublet consisting of a negative and positive lens elements,and wherein said microscope objective has the following numerical data:

    ______________________________________                                        f = 1,  NA = 0.5,  β = -40X,  WD = 2.232                                 ______________________________________                                        r.sub.1 = -3.4901                                                             d.sub.1 = 0.662                                                                              n.sub.1 = 1.7725                                                                           ν.sub.1 = 49.66                                r.sub.2 = -2.2332                                                             d.sub.2 = 0.05                                                                r.sub.3 = 8.8889                                                              d.sub.3 = 0.727                                                                              n.sub.2 = 1.497                                                                            ν.sub.2 = 81.61                                r.sub.4 = -4.0044                                                             d.sub.4 = 0.197                                                               r.sub.5 = 7.9819                                                              d.sub.5 = 1.422                                                                              n.sub.3 = 1.43389                                                                          ν.sub.3 = 95.15                                r.sub.6 = -2.824                                                              d.sub.6 = 0.453                                                                              n.sub.4 = 1.6445                                                                           ν.sub.4 = 40.8                                 r.sub.7 = 2.3314                                                              d.sub.7 = 1.022                                                                              n.sub.5 = 1.6779                                                                           ν.sub.5 = 55.33                                r.sub.8 = -6.9004                                                             d.sub.8 = 0.339                                                               r.sub.9 =  3.6048                                                             d.sub.9 = 1.246                                                                              n.sub.6 = 1.497                                                                            ν.sub.6 = 81.61                                r.sub.10 = -4.2614                                                            d.sub.10 = 0.518                                                                             n.sub.7 = 1.74                                                                             ν.sub.7 = 31.7                                 r.sub.11 = 9.972                                                              d.sub.11 = 1.189                                                              r.sub.12 = -3.3423                                                            d.sub.12 = 0.209                                                                             n.sub.8 = 1.71736                                                                          ν.sub.8 = 29.51                                r.sub.13 = 1.5201                                                             d.sub.13 = 0.276                                                                             n.sub.9 = 1.497                                                                            ν.sub.9 = 81.61                                r.sub.14 = -222.3991                                                          d.sub.14 = 0.026                                                              r.sub.15 = 1.8581                                                             d.sub.15 = 0.774                                                                             n.sub.10 = 1.78472                                                                         ν.sub.10 = 25.68                               r.sub.16 = -1.6017                                                            d.sub.16 = 0.774                                                                             n.sub.11 = 1.726                                                                           ν.sub.11 = 53.56                               r.sub.17 = 1.2426                                                             |f.sub.VVI | = 2.29, r.sub.1 /r.sub.2 = 1.56,               |r.sub.3 /r.sub.4 | = 2.22                                  |r.sub.12 /(n.sub.V-1 - 1)| = 4.66, |r.sub.17      /(1 - n.sub.VI-2)| = 1.71                                            ______________________________________                                    

where, reference symbols r₁ through r₁₇ respectively represent radii ofcurvature of respective lens surfaces, reference symbols d₁ through d₁₆respectively represent thicknesses of respective lenses and airspacesbetween respective lenses, reference symbols n₁ through n₁₁ respectivelyrepresent refractive indices of respective lenses, and reference symbolsν₁ through ν₁₁ respectively represent Abbe's numbers of respectivelenses.
 6. A microscope objective according to claim 2 wherein saidthird lens component is arranged as a cemented lens component consistingof three lens elements which are a positive, negative and positive lenselements cemented together, said fourth lens component is arranged as apositive cemented doublet consisting of a positive and negative lenselements, and said fifth lens component is arranged as a negativecemented doublet consisting of a negative and positive lens elements,and wherein said microscope objective has the following numerical data:

    ______________________________________                                        f = 1,  NA = 0.5,  β = -40X,  WD = 2.186                                 ______________________________________                                        r.sub.1 = -3.5714                                                             d.sub.1 = 0.663                                                                              n.sub.1 = 1.7725                                                                           ν.sub.1 = 49.66                                r.sub.2 = -2.2337                                                             d.sub.2 = 0.327                                                               r.sub.3 = 13.0111                                                             d.sub.3 = 0.678                                                                              n.sub.2 = 1.497                                                                            ν.sub.2 = 81.61                                r.sub.4 = -3.8674                                                             d.sub.4 = 0.342                                                               r.sub.5 = 7.47                                                                d.sub.5 = 1.374                                                                              n.sub.3 = 1.43389                                                                          ν.sub.3 = 95.15                                r.sub.6 = -2.8644                                                             d.sub.6 = 0.404                                                                              n.sub.4 = 1.6445                                                                           ν.sub.4 = 40.8                                 r.sub.7 = 2.4542                                                              d.sub.7 = 1    n.sub.5 = 1.6779                                                                           ν.sub.5 = 55.33                                r.sub.8 = -6.105                                                              d.sub.8 = 0.393                                                               r.sub.9 =  3.3165                                                             d.sub.9 = 1.198                                                                              n.sub.6 = 1.497                                                                            ν.sub.6 = 81.61                                r.sub.10 = -4.4735                                                            d.sub.10 = 0.469                                                                             n.sub.7 = 1.74                                                                             ν.sub.7 = 31.7                                 r.sub.11 = 7.302                                                              d.sub.11 = 1.13                                                               r.sub.12 = -3.4543                                                            d.sub.12 = 0.183                                                                             n.sub.8 = 1.71736                                                                          ν.sub.8 = 29.51                                r.sub.13 = 1.891                                                              d.sub.13 = 0.341                                                                             n.sub.9 = 1.497                                                                            ν.sub.9 = 81.61                                r.sub.14 = 18.8426                                                            d.sub.14 = 0.026                                                              r.sub.15 = 1.8343                                                             d.sub.15 = 0.725                                                                             n.sub.10 = 1.78472                                                                         ν.sub.10 = 25.68                               r.sub.16 = -1.8322                                                            d.sub.16 = 0.699                                                                             n.sub.11 = 1.726                                                                           ν.sub.11 = 53.56                               r.sub.17 = 1.1646                                                             |f.sub.VVI | = 2.13, r.sub.1 /r.sub.2 = 1.6,                |r.sub.3 /r.sub. 4 | = 3.36                                 |r.sub.12 /(n.sub.V-1 - 1)| = 4.82, |r.sub.17      /(1 - n.sub.VI-2)| = 1.6                                             ______________________________________                                    

where, reference symbols r₁ through r₁₇ respectively represent radii ofcurvature of respective lens surfaces, reference symbols d₁ through d₁₆respectively represent thicknesses of respective lenses and airspacesbetween respective lenses, reference symbols n₁ through n₁₁ respectivelyrepresent refractive indices of respective lenses, and reference symbolsν₁ through ν₁₁ respectively represent Abbe's numbers of respectivelenses.
 7. A microscope objective according to claim 2 wherein saidthird lens component is arranged as a cemented lens component consistingof three lens elements which are a positive, negative and positive lenselements cemented together, said fourth lens component is arranged as acemented lens component consisting of three lens elements which are anegative, positive and negative lens elements cemented together, andsaid fifth lens component is arranged as a negative cemented doubletconsisting of a negative and positive lens elements, and wherein saidmicroscope objective has the following numerical data:

    ______________________________________                                        f = 1,  NA = 0.5,  β = -40X,  WD = 2.208                                 ______________________________________                                        r.sub.1 = -3.4749                                                             d.sub.1 = 0.662                                                                              n.sub.1 = 1.76647                                                                          ν.sub.1 = 37.03                                r.sub.2 = -2.2884                                                             d.sub.2 = 0.05                                                                r.sub.3 = 9.7628                                                              d.sub.3 = 0.702                                                                              n.sub.2 = 1.497                                                                            ν.sub.2 = 81.61                                r.sub.4 = -3.6774                                                             d.sub.4 = 0.392                                                               r.sub.5 = 7.5333                                                              d.sub.5 = 1.397                                                                              n.sub.3 = 1.43389                                                                          ν.sub.3 = 95.15                                r.sub.6 = -2.6362                                                             d.sub.6 = 0.428                                                                              n.sub.4 = 1.63599                                                                          ν.sub.4 = 36.59                                r.sub.7 = 2.444                                                               d.sub.7 = 0.997                                                                              n.sub.5 = 1.68188                                                                          ν.sub.5 = 48.89                                r.sub.8 = -6.0685                                                             d.sub.8 = 0.392                                                               r.sub.9 =  3.618                                                              d.sub.9 = 0.471                                                                              n.sub.6 = 1.49791                                                                          ν.sub.6 = 55.84                                r.sub.9 ' = 2.5286                                                            d.sub.9 ' = 0.968                                                                            n.sub.6 ' = 1.497                                                                          ν.sub.6 ' = 81.61                              r.sub.10 = -2.9389                                                            d.sub.10 = 0.493                                                                             n.sub.7 = 1.75001                                                                          ν.sub.7 = 28.27                                r.sub.11 = 9.0927                                                             d.sub.11 = 0.936                                                              r.sub.12 = -3.4568                                                            d.sub.12 = 0.183                                                                             n.sub.8 = 1.70991                                                                          ν.sub.8 = 30.86                                r.sub.13 = 1.7111                                                             d.sub.13 = 0.34                                                                              n.sub.9 = 1.497                                                                            ν.sub.9 = 81.61                                r.sub.14 = 37.4012                                                            d.sub.14 = 0.026                                                              r.sub.15 = 1.8973                                                             d.sub.15 = 0.749                                                                             n.sub.10 = 1.80265                                                                         ν.sub.10 = 25.11                               r.sub.16 = -1.6842                                                            d.sub.16 = 0.724                                                                             n.sub.11 = 1.71559                                                                         ν.sub.11 =  55.05                              r.sub.17 = 1.1841                                                             |f.sub.VVI | = 2.39, r.sub.1 /r.sub.2 = 1.52,               |r.sub.3 /r.sub.4 | = 2.65                                  |r.sub.12 /(n.sub.V-1 - 1)| = 4.87, |r.sub.17      /(1 - n.sub.VI-2)| = 1.65                                            ______________________________________                                    

where, reference symbols r₁ through r₁₇ respectively represent radii ofcurvature of respective lens surfaces, reference symbols d₁ through d₁₆respectively represent thicknesses of respective lenses and airspacesbetween respective lenses, reference symbols n₁ through n₁₁ respectivelyrepresent refractive indices of respective lenses, and reference symbolsν₁ through ν₁₁ respectively represent Abbe's numbers of respectivelenses.
 8. A microscope objective according to claim 1 arranged to varythe airspace between said third lens component and said fourth lenscomponent according to the thickness of cover glass to be used in orderto thereby correct aggravation of aberrations to be caused by variationin the thickness of cover glass.